The invention relates to a helical scan cassette recorder: that is, recording and/or reproducing apparatus for a magnetic tape which is accomodated in a cassette that can be introduced into the apparatus and can be drawn out of the cassette through an opening therein, comprising a drum-shaped scanning device for the magnetic tape, around the outer surface of which the magnetic tape drawn out of the cassette can be wrapped in a given angular range; a tape tension adjustment device which comprises a tape tension indicator, and serves to adjust the tape tension when the magnetic tape wrapped around the scanning device is driven; and a tape guide device which is adapted to draw the magnetic tape out of the cassette and to wrap it around the scanning device. Such a recorder used for television signals is commonly called a VCR. The guide device typically has at least one tape guide which is secured to a holder and can be displaced between a rest position and an operating position by means of a displacement device. In the rest position the guide engages behind the magnetic tape accomodated in the at the area of the cassette opening and in the operating position the magnetic tape taken along by the guide during its displacement is kept wrapped around the scanning device. The guide device includes a positioning device for positioning the tape guide in its operating position, which is arranged on a displaceable support subjected to the force of a spring.
Such a VCR is known, for example, from U.S. Pat. No. 4,060,840. In this apparatus, the tape tension adjustment device comprises as tape tension indicator a tape tension sensor lever. Upon displacement of the tape guide by means of the displacement device from its rest position into its operating position the sensor lever is pivoted while the displacement device takes the magnetic tape from an inactive position into an active position, in which a tape tension sensor pin secured to the tape tension sensor lever presses against a portion of the magnetic tape taken along by the tape guide. This requires a comparatively laborious and complicated construction. The magnetic tape is wrapped around the tape tension sensor over a comparatively small angular range, so that the tape tension indicator does not have to the desired high sensitivity. Furthermore, the tape tension sensor pin in the travel path of the tape cooperates with the magnetic tape at a comparatively large distance from the scanning device, while several guide and scanning members engage the magnetic tape and vary the tape tension between the tape tension sensor pin and the scanning device. Therefore with this tape tension indicator it is not possible to detect the actual tape tension of the magnetic tape in the immediate proximity of the scanning device, and to adjust the tension of the magnetic tape, especially at the area of the scanning device, by means of the tape tension adjustment device.
Adjustment of the tension of the magnetic tape at the area of the scanning device is of particular importance for perfect recording and/or reproducing operation by a scanning device of the type having at least one magnetic head. For positioning the tape guide in its operating position, the apparatus shown in the U.S. patent has a positioning device provided on a displaceable support, the displaceability of the support being utilized solely for positioning purposes. Due to this displaceability of the support, the positioning device provided on this support can be automatically adapted during a positioning operation to a further positioning device for positioning the holder for the tape guide.